Commercially available video event detection systems use change detection to generate alarms. Since such systems generate an alarm when any motion occurs in the monitored area, incidental motion or change in lighting can generate false alarms. Recent advances in video monitoring technology enable the detection of more specific events than just motion, such as when a person enters a room, deposits or picks up an object, or loiters for a while in a given area. Although the events these advanced systems detect are more sophisticated than those detected via motion detection, they are still unstructured events that are detected regardless of the context in which they occur. This can result in alarms being generated on events that are not of interest.
For example, if a system is monitoring a room or store with the intention of detecting theft, the system could be set up to generate an alarm whenever an object is picked up. However, no theft has occurred unless the person leaves the area with the object. A simple, unstructured event detection system would generate an alarm every time someone picked up an object. This would result in many false alarms. Therefore there is a need in the art for a system that can recognize complex events an thus filter out false positive alarms.
Given a system which detects simple events, one can easily create a user interface that enables someone to define a complex event by constructing a list of sub-events. After one or more complex events have been defined, the sub-events of complex events defined later can be complex events themselves. As an alternative user interface, complex events could be constructed in a top-down fashion, defining the highest-level complex event first, and then recursively defining the sub-events until all of the lowest-level events are simple.
Once the user has defined the complex events and the actions to take when they occur, the event detection system must recognize these events as they occur in the monitored area. For the purposes of this application, assume a priori that the simple events can be recognized and that the object involved in them can be tracked. The preferred embodiment uses the method discussed above to recognize the simple events or any other suitable prior art technique. In order to recognize a complex event, the system must keep a record of the sub-events that have occurred thus far and the objects involved in these sub-events. Whenever the first sub-event in a complex event""s sequence is recognized, an activation for that complex event is created. The activation contains an indication of the identity of the object involved in the event. The activation also includes an index, which is the number of sub-events in the sequence that have been recognized thus far. The index is initialized to 1 when the activation is created, since the activation is only created when the first sub-event of that complex event is detected. The system maintains a list of current activations for each defined complex event type. Whenever any new event is detected, the list of current activations is consulted to see if the newly detected event matches the next sub-event in any of the currently open complex events. If so, the index for that complex event is incremented. If the index reaches the total number of sub-events in the sequence for that complex event, the complete complex event has been recognized. Thus any desired alarm is generated. Since the complex event that was just recognized may also be a sub-event of another complex event, the activation lists are consulted again to see if the indices of any other complex event activations can be advanced.